Aerodynamic supplementary device for float aircraft

ABSTRACT

The additional device according to the invention for floats for seaplanes and floatplanes comprises four airtight bladders ( 10 ) to which compressed air can be applied, and which extend along the float and rest on side surfaces ( 11 ) of the float, which essentially consists of a box ( 1 ). The bladders ( 10 ) are composed of a flexible material with little expansion capability or an elastomer material, and are entirely covered with an elastic and watertight textile skin ( 9 ). In the state when compressed air is applied, the edges of the box ( 1 ), that is to say the side edges ( 8 ) and the keel edge ( 7 ), are smoothed. Thus, as soon as the aircraft has become airborne, the drag coefficient c D  of the float can be considerably reduced. The compressed air is released for the aircraft to land on and take off from water, so that the edges ( 7, 8 ) can produce their effect for directional stability (keel edge ( 7 )) and in order to prevent the Coanda effect (side edges  8 )).

[0001] The present invention relates to an additional device forseaplanes and floatplanes according to the precharacterizing clause ofPatent claim 1. Fluid-dynamic compromises have to be made with regard tothe parts of flying boats, seaplanes, floatplanes and land aircraftprovided with floats which are located in the water during take-off andlanding; in order to avoid lengthy circumlocutions in each case, theseparts will be referred to as floats from now on. Said compromises arebased on the following considerations and requirements:

[0002] floats are intended to give the aircraft good directionalstability on water,

[0003] floats should be able to change easily from being pure buoyancyfloats to the sliding phase,

[0004] floats should have as little drag in air (c_(D)) as possible.

[0005] Technical measures which take account in particular of the firsttwo—hydrodynamic—requirements generally make the c_(D) value worse,while those which improve the c_(D) value generally destroy the buoyancyand sliding capability.

[0006] The Coanda effect (Henri Coanda 1886-1972) plays a central rolehere: on the basis of the continuity law, water flows around curvedsurfaces on a body and, in the process, its speed is increasedresulting, according to Bernoulli's Law, in a pressure drop under water.Thus, if a float has a dynamically advantageous shape, then thispressure drop results in it normally being drawn into the water,rendering a sliding phase largely impossible, both during take-off andduring landing on water.

[0007] In contrast, if a float is provided with, for example, a V-shapedlower surface, with a sharp-edged transition into vertical walls, thatis to say with a sharp bilge edge, this not only improves thedirectional stability, but also largely suppresses the Coanda effect.However, this is invariably at the expense of the c_(D) being increasedby several times. The compromise to be reached between hydrodynamic andaerodynamic maximization generally therefore needs to be made in favourof hydrodynamics.

[0008] This applies in particular to the step or the step-shaped edge onthe bottom of the float in virtually all known embodiments: this ishydrodynamically necessary in order to make the water flow turbulent andto allow air to flow in; however, it is aerodynamically disastrous sinceit likewise produces flow separation, but in this case this isundesirable.

[0009] The previously known attempts to overcome this poor compromiseare not very numerous:

[0010] either the edge—in plan view—is rounded at the rear

[0011] or an arrangement of moving flaps has been proposed which areextended in flight and in the process cover the step-shaped edge, inorder to improve the aerodynamic aspect, for example in DE 38 41 878 A1.

[0012] The object of the present invention is now to provide asupplement for hydrodynamically optimized floats, which allows the c_(D)of such floats to be improved to a major extent when the aircraft isairborne. A further object is to design such a supplement such that itis light and such that all the components which are subject to wear areeasily replaceable.

[0013] The way in which said object is achieved is described in thecharacterizing part of claim 1, with regard to the main features of theinvention, and in the following claims with regard to furtheradvantageous embodiments.

[0014] The attached drawing shows the idea of the invention withreference to a number of exemplary embodiments. In the figures:

[0015]FIGS. 1a, b, c show three cross-sectional float shapes which areknown from the prior art,

[0016]FIG. 2 shows a side view of the known float from FIG. 1a,

[0017]FIG. 3 shows a first exemplary embodiment of a supplementaccording to the invention with reference to FIG. 1a, in the form of across section,

[0018]FIG. 4 shows a second exemplary embodiment of a supplementaccording to the invention with reference to FIG. 1a, in the form of across section,

[0019]FIG. 5 shows a third exemplary embodiment of a supplementaccording to the invention with reference to FIG. 1c, in the form of across section,

[0020]FIG. 6 shows a fourth exemplary embodiment of a supplementaccording to the invention with reference to FIG. 1a, in the form of across section,

[0021]FIG. 7 shows a fifth exemplary embodiment of a supplementaccording to the invention with reference to FIG. 2, in the form of alongitudinal section, and

[0022]FIG. 8 shows a plan view of the example in FIG. 7, fromunderneath.

[0023]FIGS. 1a,b,c show three floats in the form of a cross section,such as those which are known as examples of the prior art.

[0024]FIG. 1a illustrates one frequently used profile: an essentiallyrectangular box 1 has an inverted roof-shaped profile 2 underneath; thetransition to the vertical is formed with a sharp edge, in order tosuppress the Coanda effect. The dashed line shows a round profile 3which is used as an alternative to the box 1 and which improves theaerodynamic characteristics.

[0025]FIG. 1b differs from FIG. 1a in that the roof-shaped profile 2 isin the form of a hollow keel 4, which results in improvements in termsof water spray, directional stability and sliding characteristics, butobviously, in contrast, results in an aerodynamic deterioration. Thedashed lines once again show a variant 5 of the box 1 which tapersupwards.

[0026]FIG. 1c shows what is referred to as the Dornier profile, whichhas good directional stability and sliding characteristics and islikewise optimized for water spray, but is regarded as being rather pooraerodynamically, because there are two edges 6 on each side.

[0027] The side view in FIG. 2 clearly shows an edge 12, which is alwaysprovided, irrespective of the choice of the cross-sectional profileshown in FIGS. 1a,b,c. As already indicated, the object of the edge 12is to cause flow separation in water, which is the only way in which theaircraft can lift itself off the water at all. However, it likewiseresults in flow separation in air, and this results in a greatlyincreased drag coefficient c_(D). Depending on whether the float underconsideration is the fuselage of a flying boat or the floats of aseaplane or floatplane, the c_(D) increase may be from 20% up to severaltimes that of the float under consideration. The idea of the inventionwill be explained in more detail with reference to a number of exemplaryembodiments, and based on FIGS. 3 to 8: virtually without exception, thefloats are nowadays manufactured from hard materials, such as metaland/or plastics. It is thus fundamental to the invention to provide asupplement which, if need be, be fitted retrospectively and is composedof pneumatic elements whose shape can be varied by applying compressedair and can be predetermined by material selection and cutting to size.

[0028]FIG. 3 shows a cross section of such a supplement according to theinvention, as can be fitted to a float as shown in FIG. 1a. Theroof-shaped profile 2 has two surfaces 11 and three edges 7, 8: one keeledge 7 and two side edges 8. The roof-shaped profile 2 is covered with atextile skin 9 which can expand, is coated such that it is watertightand is attached to the float in the region of the edges 7, 8. Flexiblebladders 10, running along the float, are inserted between the surfaces11 of the profile 2 and the textile skin 9, and can have compressed airapplied to them—via valves which are not shown here. The bottom of thefloat then assumes a curved shape, preferably a shape in which thesurface transitions between the bottom and the walls of the box 1 runsmoothly, and the transition from the rounded shape of one bladder 10 tothe other likewise runs smoothly. However, the side edges 8 are at leastweakened, both in their geometry and in their aerodynamic effect. Thiscan be achieved firstly by the flexible material from which the bladders10 are made being a textile material which has little expansioncapability and is coated such that it is airtight, and secondly by thebladders 10 being manufactured from an elastomer and the extent of thecurvature being set correctly in conjunction with the air pressure inthe bladders 10, on the one hand, and the stresses originating from theelasticities of the skin 9 and bladders 10. The first-mentioned varianthas the advantage that the desired shape is achieved above a specificair pressure; if the air pressure is increased further, the shape of thebladder 10 scarcely changes any further, provided the bladder 10 is, forexample, bonded to the surfaces 11 of the profile 2, at least in theregion of the edges 7, 8, over the entire length of the bladders 10.Different forms of connection in the form of a line or surface are, ofcourse, likewise included within the idea of the invention.

[0029]FIG. 4 shows a further embodiment of the idea of the invention. Inthis case, the float has four bladders 10 running over at least a majorproportion of its length. The construction, the material and theattachment of the bladders 10 correspond to what has been stated withregard to the bladders 10 in FIG. 3. The bladders 10 which areadditional to those shown in FIG. 3 rest on the side surfaces 11, whichlikewise have the number 11. The use of four bladders makes it possibleto produce smooth surface transitions over the edges 7, 8, with lessdeformation of the elastic skin 9.

[0030] If a float with the variant 5 of the box 1 illustrated in FIG. 1bis used, in which the side surfaces 11 taper inwards in the upwarddirection and the surfaces 17 are in the form of hollow keels 4, thenthe exemplary embodiment shown in FIG. 4 is preferred.

[0031]FIG. 5 illustrates an exemplary embodiment of the idea of theinvention with a Dornier profile as shown in FIG. 1c. In this case aswell, two bladders 10 can be provided, as shown, or else four as shownin FIG. 4. The essential features are the smooth transitions of the skin9 over the edges, which are anotated by the number 6 here, or—as alreadystated—with them at least being weakened.

[0032]FIG. 6 illustrates a fourth exemplary embodiment of the idea ofthe invention, in this case, by way of example, showing across-sectional profile corresponding to FIG. 1a. The longitudinallyrunning bladders 10 used here cover the two side surfaces 11 onlypartially: in each case from the side edge 8 to a longitudinal line 14(which appears as a dot here). In this area, the bladders 10 are bondedto the side surfaces 11 either over their complete area or else, forexample, in the form of a line. The entire lower surface of the float, across section of which is illustrated here, is covered with the elastictextile skin 9. When compressed air is applied to the two bladders 10,the skin 9 now touches the float only in the areas of the keel edge 7and of the side edges 8 where it is also attached. Thus, with thisexemplary embodiment, it is possible to replace the side edges 8 by asmooth transition.

[0033]FIG. 7 is a detailed illustration of the transversely running edge12 shown in FIG. 2. This edge 12, followed in the aft direction by astep 16, is required for hydrodynamic purposes since the water flowseparates here and allows the float to slide—both during the take-offand landing phases. Aerodynamically, that is to say as soon as theaircraft is airborne, the edge 12 has an extremely disturbing effect, asalready stated. FIG. 7 thus illustrates how this disturbing effect isovercome, or at least considerably reduced, according to the invention:the supplement according to the invention thus also includes anextension 13, corresponding to the cross-sectional profile, of the edge12. When the bladder 10 is not inflated, the elastic skin 9 forces itessentially behind the extension 13 into the step 16. In this case aswell, the bladder 10 is, of course, bonded to the float, for example, atleast along the boundary of its contact surface with the float. In thestate when compressed air is applied, it assumes the shape shown in FIG.7, once again resulting in a smooth transition between the surface ofthe float forward of the edge 12 and that aft of it. The transition fromsaid surface to the skin 9 covered by the bladder 10 is also smooth.This prevents flow separation in the air flowing around the float.

[0034] The extension 13 of the edge 12 is preferably attached to thefloat by bonding, with the extension being appropriately shaped andprepared for this purpose. Such bonding is, in contrast, prior art andtherefore does not need to be described here. Depending on theconfiguration of the float, it may be advantageous to provide twobladders 10 filling the step 16 rather than one bladder 10; for examplewhen using a Dornier profile.

[0035]FIG. 8 shows a plan view, from underneath, of the subject matterof FIG. 7 using only one bladder 10. The dashed line shows, firstly, theedge 12 which now projects from the extension 13 and, secondly, theboundary of the bonding of the bladder 10. If the aim is to fill onlythe step 16 by a bladder 10 with an elastic skin 9, the elastic skin 9is drawn over the bladder 10 to such an extent that a secureconnection—for example by bonding—to the lower surface of the float canbe produced, and then has an edge 15. However, if it is also intended tocarry out the smoothing of the other edges 6, 7, 8 according to theinvention, the elastic skin 9 preferably covers at least the entirelower surface of the float.

[0036] The lines for the compressed air are not shown, since they areknown per se. They are preferably routed in the interior of the float.

[0037] In order to deflate the bladders 10 quickly, vacuum lines canalso be routed to the bladders 10, so that they can be pumped out beforelanding. However, the lines which are used for the compressed air canalso be used for this purpose by providing valves which are known per seand provided a vacuum pump is present.

[0038] The supplement according to the invention may be of modular form,can be matched to the most usual types of and sizes of floats, mayinclude only the smoothing of the edge 12, but may also include thesmoothing of all the edges 6, 7, 8.

[0039] Its use is particularly advantageous for floats onlow-performance aircraft such as light aircraft and ultralights, wherethe influence of the c_(D) values of the floats being improved in thisway is noticeable.

1. Pneumatic additional device for the floats, which are provided withan edge (12) running transversely and with a step (15) produced behindthe edge (12), of seaplanes and floatplanes in order to reduce the c_(D)coefficient of the float in the air, characterized in that said devicecomprises flexible, airtight bladders (10) to which compressed air canbe applied, an elastic skin (9) which is manufactured from textilematerial and is coated such that it is watertight, with the bladders(10) optionally being arranged on the float and being covered by theskin (9) such that the surface transitions in the region of edges (6, 7,8, 12) of the float, which can lead to flow separation in the air, canbe smoothed by applying compressed air to the bladders (10). 2.Pneumatic additional device according to Patent claim 1, with the floathaving a V-shaped profile cross section in its part which enters thewater, with a keel edge (7) and two side edges (8) and surfaces (11)between the edges (7, 8) and adjacent to them, characterized in that thebladders (10) run along the float, are covered with the elastic textileskin (9) and rest on the surfaces (11).
 3. Pneumatic additional deviceaccording to Patent claim 2, characterized in that the float hasbladders (10) only on the surfaces (11) located between the edges (7,8).
 4. Pneumatic additional device according to Patent claim 3,characterized in that the bladders cover the entire surfaces (11). 5.Pneumatic additional device according to Patent claim 3, characterizedin that the bladders cover only that part of the surfaces (11) which isadjacent to the edges (8) and is bounded by a line (14) running alongthe surfaces (11).
 6. Pneumatic additional device according to Patentclaim 2, characterized in that the float has bladders (10) both on thesurfaces (11) located between the edges (7, 8) and on the surfaces (11)adjacent to the edges (8).
 7. Pneumatic additional device according toPatent claim 3, 4, 5 or 6, characterized in that the bladders (10) arearranged only forward of the transversely running edge (12). 8.Pneumatic additional device according to Patent claim 3, 4, 5 or 6,characterized in that the bladders (10) are arranged both forward of andaft of the transversely running edge (12).
 9. Pneumatic additionaldevice according to Patent claim 1, for floats with a Dornier profilecross section with four edges (6), characterized in that bladders (10)are provided running along the float, are covered with the elastictextile skin (9) and are arranged such that they are each locatedbetween two of the edges (6) located at the side.
 10. Pneumaticadditional device according to Patent claim 9, characterized in that thebladders (10) are arranged only forward of the transversely running edge(12).
 11. Pneumatic additional device according to Patent claim 9,characterized in that the bladders (10) are arranged both forward of andaft of the transversely running edge (12).
 12. Pneumatic additionaldevice according to Patent claim 1, characterized in that at least onebladder (10) is provided immediately aft of the transversely runningedge (12) and is covered with the elastic textile skin (9), thetransversely running edge (12) has an extension (13) which projects overit and is attached to the forward part of the float, the at least onebladder (10) is shaped and dimensioned such that, in the state whencompressed air is applied to it, it can compensate for the step (15)produced by the transversely running edge (12).
 13. Pneumatic additionaldevice according to one of Patent claims 3 to 11 and
 12. 14. Pneumaticadditional device according to one of Patent claims 1 to 13,characterized in that the bladders (10) are composed of a flexibletextile material which is coated such that it is impermeable to air andhas little elasticity, and are bonded, at least in places, to thesurfaces of the float on which they rest.
 15. Pneumatic additionaldevice according to one of Patent claims 1 to 13, characterized in thatthe bladders (10) are manufactured from an elastomer material. 16.Pneumatic additional device according to one of Patent claims 1 to 15,characterized in that compressed air lines are provided, and eachbladder (10) is connected to one such compressed air line.
 17. Pneumaticadditional device according to one of Patent claims 1 to 15,characterized in that the bladders (10) are designed such that they canbe evacuated.
 18. Pneumatic additional device according to Patent claim17, characterized in that vacuum lines are provided, and each bladder(10) is connected to one such vacuum line.
 19. Pneumatic additionaldevice according to Patent claims 16 and 18, characterized in thatvalves with a controller are provided, and the pressure lines and vacuumlines are one and the same and are operated by controlling said valves.